The objective of this project is to develop a biomimetic hand exoskeleton for effective hand rehabilitation post stroke. Rapid growth in the number of hand rehabilitative devices has been seen in recent years, but the use of the robotic devices has not reached its full potential due to their inherent limitations. Many devices are designed to only produce simple gross hand movements such as opening; while other devices can allow complex functional hand movements, their components are too bulky to allow concurrent hand and arm movements, a crucial component of a functional task-oriented training of the upper extremity. The actuation mechanism of these devices is often too complex to be controlled effectively. Furthermore, most existing devices cannot provide targeted assistance of impaired muscle function as they focus on restoring gross kinematics of hand function. Therefore, the PIs aim to develop a novel hand exoskeleton system that adopts a 'biomimetic approach', which can effectively reproduce within- and between-digit coordination of functional hand movements with a reduced number of actuators, and deliver targeted reinforcement (or counteraction) of muscles with deficit that contribute to abnormal kinematics/dynamics of the hand. Specifically, the following two aims will be accomplished: 1.To develop a biomimetic hand exoskeleton that generates coordinated hand movements and to validate its performance in control subjects. The proposed device will produce a range of functional hand movements with 20 exotendons, 16 for fingers and 4 for thumbs, which are controlled by 7 motors. Its feasibility to generate movements with proper spatiotemporal multi-joint coordination will be tested in subjects without neurological impairment. 2. To assess the efficacy of a 'subject-specific' targeted reinforcement method to generate functional movements of stroke survivors with the proposed device and its impact on motor control. The PIs will develop a systematic 'subject-specific' approach that quantifies specific impairment characteristics of each subject such as altered joint impedance, counteracts their adverse effects, and provides appropriate assistance to enable the patient to perform functional tasks using 'proper mechanics'. This approach is based upon a biomechanical modeling and a 'model-based' system identification technique that quantifies and properly compensates subject-specific impairment characteristics of stroke survivors. The proposed exoskeleton device will provide a range of functional task-oriented trainings to patients by effectively compensating their 'subject-specific' impairment characteristics. This study also proposes a novel method for an optimal assistance during training, i.e., targeted reinforcement of impaired musculotendons, which is expected to maximize patients' participation. Therefore, the outcome of this study is expected to greatly improve the efficacy of a hand rehabilitation training post stroke.